The Cold Spring Harbor Symposia on Quantitative Biology bring together scientists from all over the world to present and evaluate new data and ideas in rapidly moving areas of biological research. Each year, a topic is chosen that appears to be at a stage where general and intensive scrutiny and review are needed. Criteria for selection of topics are numerous, but include the rate of progress in a given field, how recent research is highlighting connections between fundamental biological mechanisms, and the potential applications of the new discoveries to human health and society. The decision to focus the 2013 Symposium on immunology reflects the enormous research progress achieved in recent years, and is intended to provide a broad synthesis of the current state of the field, setting the stage for future discoveries and application in human health and disease. The primary objective of the proposed 78th Symposium on Immunity & Tolerance is to provide a synthesis of the exciting progress and a forum for exchange of results in this broad field. The Cold Spring Harbor Symposium seeks to encourage and support the development of the next generation of immunologists by providing outstanding younger scientists with an opportunity to participate and communicate with more senior scientists. Much of the research will be presented in the form of posters by graduate students, postdoctoral fellows and junior faculty, providing young scientists with the opportunity to develop their ideas, their presentations skills, and their interactions with other members of the scientific community. Representation of women at the Symposium at both junior and senior level is important, since role models play a key role in attracting newcomers to any field. The Laboratory's childcare center can provide care facilities and services for scientists with young children. Equally, the Laboratory encourages minority scientists to attend and present their latest research. The Laboratory aims to disseminate this synthesis of current thinking to a broader audience. Thus the Symposium will benefit not only the attendees, but colleagues unable to attend who will be able to access talks via the Leading Strand video archive, while the presented papers will be available to readers of the published or online Proceedings, and interviews with leading researchers will be freely available on the world wide web for a wider global audience. The Leading Strand archive makes video recordings of the talks immediately available to colleagues of those who attended, while the proceedings of the Symposia are published by the Laboratory and thus made available to a wider audience than the scientists who attend the meeting. In-depth interviews with leading scientists undertaken during the Symposium provide an alternative snapshot of the state of current research. This series is the longest running and one of the most important records of biology since 1933.